(552e) Experimental Studies of Ignition in 40kW Co-Axial Turbulent Diffusion Oxy-Coal Jet Flames

This paper is directed towards understanding how composition of the coal transport medium (primary CO2 and O2) affects the ignition stand-off distance in 40kW co-axial turbulent diffusion, oxy-coal flames, supported in a specially designed combustion test rig, rated at 100kW. First, a methodology to define and quantify the ignition behavior of laboratory-combustor-scale turbulent pulverized coal jets was developed and is described in detail. Results are presented in the form of probability density profiles of the measured stand-off distance, as obtained from replicate runs each consisting of six thousand photo images. Multimodal behavior of the PDFs describing flame standoff distances was observed. Measured mean standoff distance and predicted ignition time were correlated. Results show that under turbulent mixing, the controlling mechanism of affecting coal jet ignition and flame stability is the molecular diffusion of O2 to the coal particle surface. Not only do these results provide qualitative insight into ignition of coal in turbulent oxy-coal flames of practical relevance, but they can also provide a basis for validation of future detailed simulations of this process.